Patent GB-857535-A (GB)
Title: Method and apparatus for offshore drilling
IPC: E21B7/128
Filed: 1959-10-01
Abstract: 857,535. Drilling oil wells. CALIFORNIA RESEARCH CORPORATION. Oct. 1, 1959 [Oct. 1, 1958], No. 33319/59. Class 85. In off-shore drilling, a well-tool, e.g. a drill string 132, is pulled down from the floating drilling platform by a towing head 88 connected to a towline 38 which passes over sheaves 66, 78, on a base assembly 34, to the winch 42. To begin with, the base assembly 34 with a length of conductor casing 32 is suspended, as shown in dotted lines in Fig. 1, from winches 42, 44. A drill string is passed down through the assembly 34 to drill the bore 30; the string is retained in the bore whilst the assembly 34 is lowered until it seats on the bottom 24; and the string is used for injecting the material for cementing the conductor casing 32. Preferably the end 80 of the towline is attached to a stationery member 86 whilst the assembly 34 is being lowered, and then is attached to the towing head; or the towing head, with the end 80 attached, may be mounted in the base assembly prior to the latter being lowered. After the withdrawal of the drill string from the assembly, a buoyancy chamber 112 in the towing head causes it to rise when permitted by the winch 42. The line 40 is disconnected, preferably before the lowering of the assembly 34. The assembly comprises a base 48, a cylindrical part 50 for the attachment of the casing 32, a cylinder 56 upstanding from the base and having a side opening 70 through which projects an arm 60 pivoted at 62 to a flared centralizing end 58 of the cylinder 56. The arm is swung by a hydraulic cylinder 72 either to dispose the tangent of the sheave 66 on the axis of the cylinder 56, or to remove, when the towing head is seated in the flare 58, the arm and sheave from the path of well tools through the assembly. The towline is attached to a swinging bail 104 pivoted on a ring 102 revoluble on anti-friction bearings on the towing head. The line of pivoting is offset from a diameter of the ring to increase the tendency of the pull of the line 38 to bring the bail into correct position to swing through the opening 70. The towing head is connected to the apparatus to be used or positioned, e.g., the drill string 132, or casing 144, by a cap 114, preferably in two half sections, bolted to the head, an enlarged part 126 preventing upward withdrawal of the string, but permitting downward movement into the bore. When the assembly 34 has been installed, the drill string 132 is pulled down and used for making a bore to accept a string of surface casing 134 which is likewise pulled down, the casing 134 having the mandrel 136 of a safety joint attached to its top end and being supported by hangers 138. The casing is cemented through a string connected thereto by the safety joint, the cementing string then being disconnected. Fig. 2 shows the towing head 88 pulling down a wellhead control equipment which is latched and sealed on to the safety joint mandrel 136. The control equipment comprises blowout preventers 140 and drilling head 142 and a length of casing 144 for attachment to the mandrel 136. An assembly 146, similar to the assembly 34, surmounts the drilling head 142 for pulling down well drilling and working apparatus into the well bore by means of a towline 168. The cylindrical support 148 has a side opening 150 through which is projectible a sheave 152 on an arm 154 pivoted at 156 and actuated by a hydraulic cylinder 158. The towing head 170 has a revoluble ring 174 with a hinged bail 176 attached to the towline 168, the ring and bail being brought positively into alignment with the opening 150 by camming surfaces 196 secured to the inside of the support 148 which engage rollers on the pivots of the bail, the rollers finally engaging detents 202. The well-working tool 193 is attached to the string 206 and is connected to the towing head by a split flange 186 bolted to the head. As the control equipment is lowered, the string 206 is lowered by a hoist on the ship until a safety joint barrel 126 within the towing head 88 engages and automatically latches on to the mandrel 136. The towline 38 now remains idle, whilst the towline 168 is used for subsequent drilling operations, during which mud forced down the string 206 returns through the line 212. An arm may project from the towing head to engage slidably with the towline, to position the towing head positively so that the bail retracts through the side opening. In this case the revoluble ring is dispensed with. A "kill" line 214 is operated by a remotely controlled valve 216. In a modification, the cylinder 72 is replaced by a spring which retracts the arm 60 from the opening 70, the line 38 being trained over sheaves so arranged that the tension in the line pulls the arm into the opening during the pull down of the towing head. A brake means on the arm engages the line to cause it to move with the arm as the latter is swung to the retracted position. In another modification, the arm 60 is dispensed with, the sheave 66 being journalled on a fixed axis in the opening 70 so that the rim of the sheave just projects into the cylinder 56. The line 38 is attached to a revoluble ring on the towing head through a cranked bail which acts cam wise during its final movements to align it properly with the opening 70. In a further modification wherein the sheave is on a fixed axis in the opening 70, the line 38 is attached through a swivel to the ring at a point near its rim. The flare 58 corrects the misalignment of the towing head due to this off-centre connection as the head is pulled down.